Morphologic and biochemical studies of patients with Reye's Syndrome have suggested that hepatic mitochondrial injury may be involved in the pathogenesis of this disease. Further understanding of the molecular mechanisms responsible for this injury may be gained by employing contemporary techniques of physical biochemistry. As one approach toward this problem, the effects of serum from patients with Reye's Syndrome on hepatic mitochondrial function will be studied, using rat liver as an experimental system. The proposed projects will examine the hypothesis that serum from patients with Reye's Syndrome contains: (i) an uncoupling factor; (ii) a factor which alters membrane physical properties; and/or (iii) a factor capable of stimulating free radical formation, which may promote membrane damage through oxidative processes. Alterations of mitochondrial function caused by characteristic Reye's Syndrome serum components, particularly ammonia and short chain fatty acids, will also be examined. As an alternative approach, the effects of acute and chronic treatment of rats with 4-pentenoic acid on hepatic mitochondrial function will be characterized as a possible animal model of the hepatocyte mitochondrial abnormalities which accompany Reye's Syndrome. Isolated mitochondria, phosphorylating submitochondrial particles, and suspensions of intact hepatocytes will be studied to assess mitochondrial function at different levels of structural organization. Oxidative phosphorylation, ion transport, the electrochemical proton gradient, membrane fluidity, mechanisms of superoxide and H2O2 formation, and lipid peroxidation will be studied using polarographic measurement of oxygen, high sensitivity pH recording, radioisotopic ion distribution, dual wavelength absorption spectroscopy, fluorescence, electron spin resonance, and light scattering in conjunction with extrinsic molecular probes of specific biochemical reactions. The studies will characterize the molecular mechanisms by which Reye's Syndrome serum factor(s) and components, and pentenoic acid treatment of rats, alter mitochondrial structure and function in vitro. These studies may contribute toward eventual understanding of the pathogenesis of Reye's Syndrome.